A variety of reactors has been used to process semiconductor substrates. For modern high throughput reactors, a robot is used to load and unload substrates in a reactor. To facilitate loading and unloading, substrate support pins were used in the susceptor. In an RTP reactor, such as that described in U.S. Pat. No. 5,710,407, which is incorporated herein by reference in its entirety, pins 101A and 101B (FIGS. 1A and 1B) were mounted in susceptor 102. Each of pins 101A and 101B had a tapered surface that mated with a complementary tapered surface of an opening through susceptor 102. Several mounting rods 112A and 112B were placed in the bottom of the reaction chamber 110.
When susceptor 102 was in the processing position as shown in FIG. 1A, wafer support pins 101A and 101B were seated in the susceptor openings. This prevented gas flow through the opening in the susceptor and thus prevented backside depositions.
To lift a wafer, susceptor 102 was positioned so that wafer support pins 101A and 101B were positioned above mounting rods 112A and 112B, respectively. Susceptor 102 was lowered and mounting rods 112A and 112B entered the holes in susceptor 102 from the backside and engaged wafer support pins 101A and 101B, respectively, as shown in FIG. 1B. As susceptor 102 was lowered further, wafer support pins 101A and 101B could not move lower because pins 101A and 101B were held in place by mounting rods 112A and 112B. Consequently, wafer support pin 101A and 101B held wafer 111 above susceptor 102 so that a robot could access wafer 111.
While this configuration was a significant advance over other techniques in use, the method required alignment of mounting rods 112A and 112B with the through holes in susceptor 102. Also, sometimes one or more of substrate support pins 101A and 101B did not seat properly in the susceptor opening and permitted gas flow through the opening. This resulted in a backside deposition. Since the pin was located under the wafer, the discontinuity introduced by the pin affected the uniformity of the heat distribution.
An alternative design eliminated the need for the alignment, and eliminated the heat distribution issues. In this design, the mounting rod was eliminated, and a rod was formed as a part of substrate support pin 201, as illustrated in FIG. 2A. The location of the substrate support pins was moved from under the substrate into a substrate surround ring. Thus, when the susceptor was lowered, the rod portion of each of substrate support pins 201A to 201D contacted the bottom of the reaction chamber and lifted substrate surround ring 210, and consequently the substrate above the rest of the susceptor as shown in FIG. 2B. A more complete description of FIGS. 2A and 2B is given in U.S. Pat. No. 5,820,686, which is incorporated herein by reference in its entirety.
While this design was an improvement over the design in FIGS. 1A and 1B, one or more of substrate support pins 201A to 201D sometimes did not seat properly in the susceptor, and so the substrate surround ring and consequently the supported substrate was not in the same plane as other substrates on the susceptor. If only a single substrate was being processed, the substrate was not level. In both cases, gas flowed unto the backside of the substrate, and process uniformity on the topside of the substrate was affected by the tilt introduced by the failure of the substrate support pin to seat properly. Both of these effects are undesirable. Thus, while substrate support pins 201A to 201D improved process uniformity over pins 101A and 101B, pins 201A to 201D are still a factor that can limit the overall process uniformity from wafer to wafer within a batch as well as from batch to batch whenever any one of the pins does not seat properly during the process cycle.